10 m end-fed, communal TV aerial, and an angry neighbour
You run 100 W on 28 MHz from a third-floor flat in a suburb of Athens. The antenna is a half-wave end-fed: a 9:1 transformer bolted to the balcony rail, a radiating wire sloping up to a 6 m fibreglass pole, and a 3 m counterpoise lying along the rail. SWR is 1.4:1 across the SSB segment. The RG-58 feeder runs about 7 m to the shack, parallel to and within 0.5 m of the building's communal DVB-T2 downlead. There is no common-mode choke at the feedpoint and no low-pass filter after the PA.
The neighbour one floor down complains that her television freezes and the audio drops each time you transmit SSB on 10 m; her stereo amplifier also buzzes. When you switch to a 50 Ω dummy load she has no problem at all. She has complained to the building manager, who now asks you to stop operating.
1. Decide whether the trouble is harmonic radiation, transmitter splatter, or fundamental overload of her equipment. Describe the tests you would run and what result would point to each cause.
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What the dummy-load test already proves. With a 50 Ω load the neighbour notices nothing, so the disturbance is carried by the radiated field, not by the mains or by a conducted path through the building wiring. That rules out the PSU and the shack earth as the main cause, but it does not separate harmonics, splatter and overload - all three vanish with a dummy load.
Harmonics. The DVB-T2 band is roughly 470–694 MHz; harmonics of 28 MHz landing there are the 17th to 24th. Listen with a general-coverage receiver or a spectrum analyser and a sniffing probe at 56.0 and 84.0 MHz near the antenna while you key. With no low-pass filter fitted this is a cheap hypothesis to kill: a few tens of dB of harmonic suppression may be all that is needed.
Splatter / ALC. Splatter is only a few kHz wide and appears when the audio is driven hard. Repeat the transmission with reduced mic gain and with a two-tone test; if the neighbour's symptom is unchanged, splatter is not the cause. Her report that the picture freezes for the whole transmission, even at low speech level, points away from splatter.
Fundamental overload. The decisive clue is that her UHF channel bears no harmonic relation to 28 MHz, yet her stereo buzzes too. That is RF picked up on her own wiring and rectified in a semiconductor junction in the TV tuner or audio input. Confirm by testing on another band (for example 21 MHz) and at low power: if she still sees it, the mechanism is near-field overload, not a transmitter product.
2. Give a remediation plan in priority order, with the physical reason for each step.
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1. Break the common-mode path at the feedpoint. An end-fed with a 9:1 transformer and a short counterpoise makes the outside of the coax part of the antenna circuit. Fit a 1:1 current choke (a ferrite core with 8–12 turns of the coax, or a commercial current balun) right at the transformer. This stops the feeder from radiating in the balcony area, which is the field your neighbour is sitting in.
2. Move the coupling path. Your coax runs 7 m parallel to and 0.5 m from the communal downlead - that is a transformer. Reroute it, cross the downlead at right angles, and get as much separation as the building allows.
3. Add a low-pass filter with a cut-off near 30 MHz at the transceiver output. It costs little, protects against the harmonic path described above, and removes one variable permanently.
4. Reduce the field at her window by lowering power during tests and by orienting the sloping wire away from her flat.
5. Treat her installation, with permission. Ferrite clamps on the TV mains lead and on the downlead at the TV, and a high-pass/band-stop filter at the aerial socket, will reject HF before it reaches the tuner. These parts of the communal system should not be altered without the building's consent.
6. Re-test, log results, and iterate. Change one item at a time so you can tell the neighbour, and later the regulator, what actually worked.
3. The manager asks who is legally responsible and whether you must stop. Explain your position correctly.
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Your position rests on two separate obligations that are often confused.
Your obligation is to operate a station that complies with the terms of your licence, with the technical conditions attached to it and with EMC requirements, and to take reasonable technical measures when your transmissions disturb reception. A station that passes its harmonic and spurious limits, uses a proper antenna system and a clean transmitter is being operated correctly; interference caused by the inadequate immunity of a neighbour's receiver is not automatically your fault.
Her obligation is that her television and hi-fi should meet the immunity standards applicable to consumer equipment. A TV that collapses at ordinary field strengths is a deficient installation. In practice, though, the fastest way to end the dispute is usually a choke and a filter on her side as much as on yours.
Practical position. The building manager has no authority to decide the matter and you should not simply stop transmitting to keep the peace: that concedes a fault you may not have. Cooperate, document each test and each change, keep the power down while you investigate, and do not modify the communal aerial system without consent. If the dispute continues, the national regulator (EETT) is the body that handles interference complaints and can measure your station; its findings, not the manager's opinion, settle the technical question. Keep a written log with dates, times, bands and the effect of each modification.